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A type parameter is a named variable ranging over admissible types in a generic definition. Instantiation substitutes a particular type argument, allowing one declaration to retain type information across uses. An upper type bound restricts the admissible arguments; a variance annotation instead describes how instantiated types participate in subtyping.

An upper type bound $A<:B$ requires the type argument assigned to $A$ to be a subtype of $B$. Two independently bounded parameters can retain different precise component types while sharing the same upper bound. Bounds and type variance answer different questions: admissible arguments versus subtyping between instantiations.